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Date:   Thu, 20 Dec 2018 00:39:18 +0100
From:   Oscar Salvador <osalvador@suse.de>
To:     Wei Yang <richard.weiyang@gmail.com>
Cc:     akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz,
        pavel.tatashin@microsoft.com, rppt@linux.vnet.ibm.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm, page_alloc: Fix has_unmovable_pages for HugePages
Message-ID: <20181219233914.2fxe26pih26ifvmt@d104.suse.de>
References: <20181217225113.17864-1-osalvador@suse.de>
 <20181219142528.yx6ravdyzcqp5wtd@master>
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On Wed, Dec 19, 2018 at 02:25:28PM +0000, Wei Yang wrote:
> >-			iter = round_up(iter + 1, 1<<compound_order(page)) - 1;
> >+			skip_pages = (1 << compound_order(head)) - (page - head);
> >+			iter = round_up(iter + 1, skip_pages) - 1;
> 
> The comment of round_up says round up to next specified power of 2.  And
> second parameter must be a power of 2.
> 
> Look skip_pages not satisfy this.

I thought that gigantic pages were always allocated on 1GB aligned.
At least alloc_gigantic_page() looks for 1GB range, aligned to that.
But I see that in alloc_contig_range(), the boundaries can differ.

Anyway, unless I am missing something, I think that we could just
get rid of the round_up() and do something like:

<--
skip_pages = (1 << compound_order(head)) - (page - head);
iter = skip_pages - 1;
-->

which looks more simple IMHO.

It should just work for 2MB and 1GB Hugepages.
-- 
Oscar Salvador
SUSE L3